Despite the long history of crops such as hemp, hops and cannabis the drying and curing has not changed significantly over the years. Crops such as Hemp and Cannabis are grown, feminized and harvested by cutting the plant at the stalk. Hops, or humulus lupulus belongs to the family Cannabaceae of which Cannabis sativa is also a member. The hop female bears fruit that are important product in beer brewing. These plants are dried to lower the residual water content of less than 10 wt % and ideally around 7 wt % so as to stop the growth of mold and mildew. In the case of Hemp, if the female is allowed to continue to be in the flowering stage before harvest the wt % of Tetrahydrocannabinol (THC) will increase. The production of THC is a result of the female's reproductive cycle. If the concentration THC, a bioactive regulated drug, is allowed to exceed 0.3 wt % regulators will mandate destruction of the crop. The harvest can be limited by the drying of the crop in the case of hemp so either more indoor areas for drying is required or more rapid drying techniques are required.
With these lipid rich crops in recent years a trend has been to extract oil compounds from these plants and use them as flavorings or active drug ingredients. For example, hops is now extracted with super critical extraction from the plant and the oil concentrate is added to beer during fermentation. In recently years the consumption of cannabis has been changing to a form of concentrates as opposed to flower that is ignited and smoked. Hemp, as well, is processed by extraction for the purpose of capturing CBD and terpenes for use in medicinal products and health products. There are many methods to carry out extraction of the active compounds that include polar and non-polar solvents.
A popular method of extraction of the active compounds CBD, THC and terpenes is the use of (ETOH) Ethyl Alcohol. This solvent is a readily available polar solvent that can quickly extract target compounds. This solvent is fast but not selective in that it also extracts unwanted compounds such as chlorophyll, wax, lignin and heavy metals. Thus there is a trade off in rapid up front extraction with ETOH with added equipment and labor needed in the post processing.
Super critical fluid extraction (SFE) is a popular technique of extracting non-polar oleoresin based extracts. The carbon dioxide acts as a non-polar solvent and is attracted to non-polar organic molecules such as THC, CBD, fats and lipids. Because the solvent is non polar, selectivity involving the extracts can be created by selection of process parameters such that unwanted chemicals are not extracted such as chlorophyll. Several parameters have an impact on the processing time such as temperature, pressure, solvent flow rate. The equipment used in SFE is more expensive than ETOH extraction equipment due to the need for higher operating pressures.
A recent push in the SFE industry for cannabis has been to increase the mass flow rate of the CO2 solvent where equipment manufacturers are moving away from air driven pumps and toward piston driven liquid pumps. The overall push is to minimize the hours per pound that SFE can extract cannabis, hemp or hops. This will aid the extraction process during the start-up phase when the solubility limit of the solvent can be reached due to large availability of target organic compounds. After this initial period, the rate limiting step becomes the step involving diffusion of the CO2 solvent into the intracellular material of the plant and the trichome, then back into the mobile solvent phase.
With the above mentioned techniques of processing these oil rich crops, it is common in the industry that daily throughput of cannabis extraction be up to 100 lbs/day assuming approximately 30 min/lb for CO2 extraction. This may require some $0.5 million in equipment investment. Additionally it may require a similar investment $0.5 million or double $1.0 million for the drying equipment to speed up drying an curing.
As extraction techniques are scaling up there must be drying techniques that match the production rate of the extraction techniques. Some faster drying equipment is being offered including larger convective ovens, microwave energy, or hot nitrogen blanket drying equipment. By applying thermal or microwave energy to the plant to accelerate drying, heating of the plant matrix will occur. With the additional heating and substrate temperature rise, some of the more volatile terpene compounds may be lost such as mono terpenes and sesquiterpines or other bioactive compounds can be altered. The terpenes themselves, when captured and isolated, can be sold at values nearly equivalent to the targeted oleoresin target compounds such as Tetrahydrocannabinol (THC) and cannabidiol (CBD). Thus it is beneficial to devise a chemical processing scheme that is faster and captures terpenes.
When speeding up the drying and extraction process it would be ideal to overcome two limitations of other techniques. Preservation of thermally liable headspace compounds and the fundamental limitation of diffusion kinetics during extraction. The intent of the inventors work is to create a methodology that minimizes the capital investment in equipment but creates a rapid drying and extraction method in a single production line. The current disclosure reveals methods to increase production through put by several fold with techniques that preserve headspace compounds and reduce diffusion kinetics limitation.